Microelectromechanical systems (MEMS) are devices with overall dimensions typically less than a millimeter, and individual feature sizes on the order of microns. MEMS are fabricated using integrated-circuit (IC) technology enhanced with silicon micromachining, laser machining, laser-chemical micro maching, non-planar lithography, or micro-electro-discharge machining (micro-EDM). Polishing is essential for making very fine, well defined micro-sized structures, because some of the fabrication methods listed above often produce very rough surfaces.
Polishing micro-sized structures is very different from polishing macro-sized structures. A special method is required to obtain a fine surface finish in micro-sized structure.
When general electroplating methods are applied to polish a substrate that contains a micro-sized structure, the electrical current used in electropolishing tends to concentrate at the sharp corners and features. This results in material being etched off at the sharp features, and rounding of the features The surfaces of the micro-sized structures, however, either remain rough, if the micro-sized features are not as sharp as the corners of the macro features; or the micro-sized features are destroyed before being polished; if the corners of the substrate are not very sharp (for example, if a ballshaped substrate is used).
One solution is polishing of micro-sized structures using a micro-EDM machine--the same tool that may be used to produce the micro-sized structures. The need for specialized micro-EDM machine, with sophisticated controls and specially made micro-sized electrodes, make this method difficult. Also the need to polish one feature at a time makes polishing by this method cost prohibitive.